From the Super Mario Wiki
Herbert is a Boo in Paper Mario. When Mario arrives in Gusty Gulch, a Boo named Stanley informs him that Tubba Blubba had eaten Herbert during his visit the other day. After Tubba Blubba is defeated all the Boos that he had eaten are released from his body, Herbert included. By speaking to him when returning to the gulch, it is revealed that his ancestors once lived in Tubba Blubba's Castle.